Radiation-sensitive compositions and elements with solvent resistant poly(vinyl acetal)s

ABSTRACT

A radiation-sensitive composition can be used to prepare positive-working imageable elements having improved solvent resistance and is useful for making lithographic printing plates. The composition includes an alkaline soluble polymeric binder that is a specific poly(vinyl acetal) that exhibits improved resistance to press chemicals, and a radiation absorbing compound.

CROSS-REFERENCE TO RELATED APPLICATION

This is a Continuation of application Ser. No. 11/769,766, filed Jun.28, 2007 now U.S. Pat. No. 7,723,012.

FIELD OF THE INVENTION

This invention relates to radiation-sensitive compositions andpositive-working imageable elements prepared using these compositions.It also relates to methods of imaging these elements to provide imagedelements that can be used as lithographic printing plates.

BACKGROUND OF THE INVENTION

In lithographic printing, ink receptive regions, known as image areas,are generated on a hydrophilic surface. When the surface is moistenedwith water and ink is applied, the hydrophilic regions retain the waterand repel the ink, the ink receptive regions accept the ink and repelthe water. The ink is then transferred to the surface of suitablematerials upon which the image is to be reproduced. In some instances,the ink can be first transferred to an intermediate blanket that in turnis used to transfer the ink to the surface of the materials upon whichthe image is to be reproduced.

Imageable elements useful to prepare lithographic (or offset) printingplates typically comprise one or more imageable layers applied over ahydrophilic surface of a substrate (or intermediate layers). Theimageable layer(s) can comprise one or more radiation-sensitivecomponents dispersed within a suitable binder. Following imaging, eitherthe exposed regions or the non-exposed regions of the imageable layer(s)are removed by a suitable developer, revealing the underlyinghydrophilic surface of the substrate. If the exposed regions areremoved, the element is considered as positive-working Conversely, ifthe non-exposed regions are removed, the element is considered asnegative-working. In each instance, the regions of the imageablelayer(s) that remain are ink-receptive, and the regions of thehydrophilic surface revealed by the developing process accept water oraqueous solutions (typically a fountain solution), and repel ink.

Similarly, positive-working compositions can be used to form resistpatterns in printed circuit board (PCB) production, thick-and-thin filmcircuits, resistors, capacitors, and inductors, multichip devices,integrated circuits, and active semiconductive devices.

“Laser direct imaging” methods (LDI) have been known that directly forman offset printing plate or printing circuit board using digital datafrom a computer, and provide numerous advantages over the previousprocesses using masking photographic films. There has been considerabledevelopment in this field from more efficient lasers, improved imageablecompositions and components thereof.

Thermally sensitive imageable elements can be classified as those thatundergo chemical transformation(s) in response to, exposure to, oradsorption of, suitable amounts of thermal energy. The nature ofthermally induced chemical transformation may be to ablate the imageablecomposition in the element, or to change its solubility in a particulardeveloper, or to change the tackiness or hydrophilicity orhydrophobicity of the surface layer of the thermally sensitive layer. Assuch, thermal imaging can be used to expose predetermined regions of animageable layer that can serve as a lithographic printing surface orresist pattern in PCB production.

Positive-working imageable compositions containing novolak or otherphenolic polymeric binders and diazoquinone imaging components have beenprevalent in the lithographic printing plate and photoresist industriesfor many years. Imageable compositions based on various phenolic resinsand infrared radiation absorbing compounds are also well known.

A wide range of thermally-sensitive compositions that are useful inthermal recording materials are described in patent GB 1,245,924(Brinckman), whereby the solubility of any given area of the imageablelayer in a given solvent can be increased by the heating of the layer byindirect exposure to a short duration high intensity visible lightand/or infrared radiation transmitted or reflected from the backgroundareas of a graphic original located in contact with the recordingmaterial. Several systems are described that operate by many differentmechanisms and use different developers ranging from water tochlorinated organic solvents. Included in the disclosed aqueousdevelopable compositions are those that comprise a novolak type phenolicresin. Coated films of such resins are said to show increased solubilityupon heating. The compositions may also contain heat-absorbing compoundssuch as carbon black or Milori Blue (C.I. Pigment Blue 27) toadditionally color the images.

Thermally imageable, single and/or multi-layer elements are alsodescribed in WO 97/39894 (Hoare et al.), WO 98/42507 (West et al.), WO99/11458 (Ngueng et al.), U.S. Pat. No. 5,840,467 (Kitatani), U.S. Pat.No. 6,060,217 (Ngueng et al.), U.S. Pat. No. 6,060,218 (Van Damme etal.), U.S. Pat. No. 6,110,646 (Urano et al.), U.S. Pat. No. 6,117,623(Kawauchi), U.S. Pat. No. 6,143,464 (Kawauchi), U.S. Pat. No. 6,294,311(Shimazu et al.), U.S. Pat. No. 6,352,812 (Shimazu et al.), U.S. Pat.No. 6,593,055 (Shimazu et al.), U.S. Pat. No. 6,352,811 (Patel et al.),U.S. Pat. No. 6,358,669 (Savariar-Hauck et al.), and U.S. Pat. No.6,528,228 (Savariar-Hauck et al.), and U.S. Patent ApplicationPublications 2002/0081522 (Miyake et al.) and 2004/0067432 A1 (Kitson etal.).

The industry has focused on the need to diminish the solubility of theexposed regions of phenolic binders (dissolution inhibitors) in theimageable layers before exposure and to enhance their solubility afterexposure to suitable thermal energy (dissolution enhancers). WO2004/081662 (Memetea et al.) describes the use of various phenolicpolymers or poly(vinyl acetals) in combination withdevelopability-enhancing compounds of an acidic nature inpositive-working compositions and elements. Some particular poly(vinylacetals) useful in this manner are described in U.S. Pat. No. 6,255,033(Levanon et al.) and U.S. Pat. No. 6,541,181 (Levanon et al.).

Some useful poly(vinyl acetals) are described in U.S. Ser. No.11/677,599 (filed Feb. 22, 2007 by Levanon et al.), EP 1,627,732A1(Hatanaka et al.), and U.S. Published Patent Applications 2005/0214677(Nagashima), 2005/0214678 (Nagashima), and 2006/0275698 (My T. Nguen)

Problem to be Solved

Offset printing plates recently have been the subject of increasingperformance demands with respect to resistance to solvents and commonprinting room chemicals. Printing plates encounter pressroom chemicalssuch as plate cleaning agents, blanket washing agents, and alcoholsubstitutes in the fountain solution. Particularly in printing processesusing ultraviolet-curable inks, where rinsing agents with a high contentof esters, ethers or ketones are used, the chemical resistance ofconventional positive-working printing plates can be improved.

Imaged regions in such printing plates should be substantially insolublein ultraviolet-curable inks and substantially insoluble in solvents,often glycol ethers, used to clean plates during or after a print run.Conventional quinone diazide/phenolic resin-based radiation-sensitivecompositions are soluble in glycol ether solvents, and are disfavoredfor printing with ultraviolet-curable inks.

Another demand is that the imaged regions be substantially insoluble inthe fountain solutions (or dampening liquids) that are used to wet thehydrophilic areas of the plates. Conventional fountain solutions arelargely made up of water and a small amount of alcohol. More recently,such fountain solutions have been replaced, in some situations, withformulations comprising alternative additives in order to removeinflammable alcohol solvents from press room environments. Additivesthat have been used in this manner include surfactants and variousnon-volatile solvents that may be more aggressive towards theradiation-sensitive compositions. Conventional radiation-sensitivecompositions are relatively susceptible to attack by replacementfountain solutions.

A need remains for positive-working, thermally imageable elements thathave improved bakeable and improved resistant to press chemistries, suchas lithographic inks, fountain solutions, and the solvents used inwashes, such as UV washes. Bakeability is highly desirable becausebaking increases the press run length for the printing plates.

SUMMARY OF THE INVENTION

The present invention solves the noted problem with a novel compositionand positive-working element. Thus, the present invention provides aradiation-sensitive composition comprising:

a. an alkaline soluble polymeric binder, and

b. a radiation absorbing compound,

the alkaline soluble polymeric binder being a poly(vinyl acetal) thatcomprises recurring units that are represented by the followingStructure (I):-(A)_(m)-(B)_(n)-  (I)wherein:

-   -   A represents recurring units represented by the following        Structure (Ia):

-   -   B represents recurring units represented by the following        Structure (Ib):

-   -   R and R′ are independently hydrogen or a substituted or        unsubstituted alkyl, substituted or unsubstituted cycloalkyl, or        halo group,    -   R¹ is a substituted or unsubstituted phenol, substituted or        unsubstituted naphthol, or substituted or unsubstituted        anthracenol group,    -   R² is a substituted or unsubstituted naphthol but is different        from R¹,    -   m is at least 20 mol %, n is at least 10 mol %, and    -   the radiation-sensitive composition further comprising a        developability-enhancing composition.

This invention also provides a positive-working imageable elementcomprising a substrate having thereon an imageable layer comprising analkaline soluble polymeric binder, and a radiation absorbing compound,wherein the alkaline soluble polymeric binder is a poly(vinyl acetal)comprising recurring units that are represented by Structure (I) or(I-A) defined herein.

Further, a method of making a printing plate comprises:

-   -   A) imagewise exposing a positive-working imageable element of        the present invention to provide exposed and non-exposed        regions, and    -   B) developing the imagewise exposed element to remove only the        exposed regions.

The positive-working compositions and imageable elements of thisinvention exhibit improved resistance to press chemicals and require nopre-heating step before development. In addition, we found that theimageable elements have improved sensitivity, run length on-press, andbakeability. These advantages have been achieved by using a particularclass of alkaline soluble poly(vinyl acetal) binders in the imageablelayer that have improved resistance to the press chemicals.

DETAILED DESCRIPTION OF THE INVENTION

Definitions

Unless the context otherwise indicates, when used herein, the terms“radiation-sensitive composition” and “imageable element” are meant tobe references to embodiments of the present invention.

In addition, unless the context indicates otherwise, the variouscomponents described herein such as “poly(vinyl acetal)”, “radiationabsorbing compound”, “secondary polymeric binder”, and“developability-enhancing compound”, also refer to mixtures of eachcomponent. Thus, the use of the articles “a”, “an”, and “the” is notnecessarily meant to refer to only a single component.

Unless otherwise indicated, percentages refer to percents by weight.

The term “single-layer imageable element” refers to imageable elementsthat require only one layer for imaging, but as pointed out in moredetail below, such elements may also include one or more layers under orover (such as a topcoat) the imageable layer to provide variousproperties.

As used herein, the term “radiation absorbing compound” refers tocompounds that are sensitive to certain wavelengths of radiation and canconvert photons into heat within the layer in which they are disposed.These compounds may also be known as “photothermal conversionmaterials”, “sensitizers”, or “light to heat convertors”.

For clarification of definition of any terms relating to polymers,reference should be made to “Glossary of Basic Terms in Polymer Science”as published by the International Union of Pure and Applied Chemistry(“IUPAC”), Pure Appl. Chem. 68, 2287-2311 (1996). However, any differentdefinitions set forth herein should be regarded as controlling.

The terms “polymer” and “poly(vinyl acetal) refer to high and lowmolecular weight polymers including oligomers and includes bothhomopolymers and copolymers.

The term “copolymer” refers to polymers that are derived from two ormore different monomers, or have two or more different recurring units,even if derived from the same monomer.

The term “backbone” refers to the chain of atoms in a polymer to which aplurality of pendant groups are attached. An example of such a backboneis an “all carbon” backbone obtained from the polymerization of one ormore ethylenically unsaturated polymerizable monomers. However, otherbackbones can include heteroatoms wherein the polymer is formed by acondensation reaction of some other means.

Uses

The radiation-sensitive compositions of this invention can be used toform resist patterns in printed circuit board (PCB) production,thick-and-thin film circuits, resistors, capacitors, and inductors,multi-chip devices, integrated circuits, and active semi-conductivedevices. In addition and preferably, they can be used to providepositive-working imageable elements that in turn can be used to providelithographic printing plates. Other uses would be readily apparent toone skilled in the art.

Radiation-Sensitive Compositions

The radiation-sensitive compositions include one or more alkalinesoluble polymeric binders that are poly(vinyl acetal)s as defined below.These poly(vinyl acetal)s are considered the “primary” polymeric binderspresent in the composition or imageable layer. The weight averagemolecular weight (M_(w)) of the useful polymers is generally at least5,000 and can be up to 300,000 and typically from about 20,000 to about50,000. The optimal M_(w) may vary with the specific polymer and itsuse.

The alkaline soluble primary polymeric binder is a poly(vinyl acetal)that comprises recurring units that are represented by the followingStructure (I):-(A)_(m)-(B)_(n)-  (I)wherein:

-   -   A represents recurring units represented by the following        Structure (Ia):

-   -   B represents recurring units represented by the following        Structure (Ib):

In some embodiments, the useful poly(vinyl acetal)s further compriserecurring units that are represented by one or more of the followingStructures (Ic), (Id), (Ie), (If), and (Ig):

In the above structures, R and R′ are independently hydrogen, or asubstituted or unsubstituted linear or branched alkyl group having 1 to6 carbon atoms (such as methyl, ethyl, n-propyl, n-butyl, n-pentyl,n-hexyl, chloromethyl, trichloromethyl, iso-propyl, iso-butyl, t-butyl,iso-pentyl, neo-pentyl, 1-methylbutyl and iso-hexyl groups), orsubstituted or unsubstituted cycloalkyl group having 3 to 6 carbon atomsin the ring (such as cyclopropyl, cyclobutyl, cyclopentyl,methylcyclohexyl, and cyclohexyl groups), or a halo group (such asfluoro, chloro, bromo, or iodo). Typically, R and R′ are independentlyhydrogen, or a substituted or unsubstituted methyl or chloro group, orfor example, they are independently hydrogen or unsubstituted methyl.

R¹ is a substituted or unsubstituted phenol, a substituted orunsubstituted naphthol, or a substituted or unsubstituted anthracenolgroup. These phenol, naphthol, and anthracenol groups can have up to 3additional substituents including additional hydroxy substituents,methoxy, alkoxy, aryloxy, thioaryloxy, halomethyl, trihalomethyl, halo,nitro, azo, thiohydroxy, thioalkoxy, cyano, amino, carboxy, ethenyl,carboxyalkyl, phenyl, alkyl, alkenyl, alkynyl, cycloalkyl, aryl,heteroaryl, and heteroalicyclic groups. For example, R¹ can be anunsubstituted phenol or naphthol group such as a 2-hydroxyphenyl or ahydroxynaphthyl group.

R² is a substituted or unsubstituted naphthol group. It can have up to 3additional substituents as described above for R¹. In addition, R² isdifferent from R¹.

R³ is a substituted or unsubstituted alkynyl group having 2 to 4 carbonatoms (such as ethynyl groups), or a substituted or unsubstituted phenylgroup such as carboxy-substituted phenyl groups (including phenyl,4-carboxyphenyl, carboxyalkyleneoxyphenyl, and carboxyalkylphenylgroups).

R⁴ is an —O—C(═O)—R⁵ group wherein R⁵ is a substituted or unsubstitutedalkyl group having 1 to 12 carbon atoms or substituted or unsubstitutedaryl group having 6 or 10 carbon atoms in the aromatic ring (such assubstituted or unsubstituted phenyl and naphthyl groups, includingphenyl, xylyl, tolyl, p-methoxyphenyl, 3-chlorophenyl, and naphthyl).Typically, R⁵ is a substituted or unsubstituted alkyl group having 1 to6 carbon atoms such as an unsubstituted methyl or ethyl group.

R⁶ is a hydroxy group.

R⁷ is the following group:

wherein X is a direct single bond or a —O—CH₂— group.

It would also be apparent to one skilled in the art that while R⁷ isillustrated above in an “unopened” form (that is, with a fused ring), itcan also exist in the “opened” form wherein there is no heterocyclicring and there is no bond between the —CH< group and the phenyl ring,and the additional carbon valence is replaced with a hydrogen atom.Thus, the “opened” and “unopened” forms of R⁷ are considered equivalentfor purposes of this invention.

In Structure (I), m is at least 20 mol % and typically at least 30 mol %or from about 50 to about 80 mol %, n is at least 10 and typically atleast 20 mol %. The sum of m and n (m+n) can be as high as practicallypossible, but in some embodiments this sum is less than or equal to 75mol % and typically less than or equal to 60 mol %.

When the recurring units represented by Structures (Ic), (Id), (Ie),(If), and (Ig) are present in the polymeric binder in the followingamounts:

from about 2 to about 10 mol % of recurring units represented byStructure (Ic),

from about 2 to about 25 mol % of recurring units represented by eitheror both of Structures (Id) and (Ie),

from about 1 to about 15 mol % of recurring units represented byStructure (If), and

from about 15 to about 30 mol % of recurring units represented byStructure (Ig).

In some embodiments, the alkaline soluble polymeric binder isrepresented by the following Structure (I-A):-(A)_(m)-(B)_(n)-(C)_(p)-(D)_(q)-(E)_(r)-(F)_(s)-(G_(t)-  (I-A)wherein:

-   -   A represents recurring units represented by the following        Structure (Ia):

-   -   B represents recurring units represented by the following        Structure (Ib):

-   -   C represents recurring units represented by the following        Structure (Ic):

-   -   D represents recurring units represented by the following        Structure (Id):

-   -   E represents recurring units represented by the following        Structure (Ie):

-   -   F represents recurring units represented by the following        Structure (If):

-   -   G represents recurring units represented by the following        Structure (Ig):

wherein R and R′, R¹, R², R³, R⁴, R⁵, R⁶, and R⁷ are as defined above,

-   -   m is at least 30 mol %, n is at least 20 mol %, the sum of m and        n (m+n) is less than or equal to 60 mol %,    -   p is from about 2 to about 10 mol %,    -   q and r are independently from about 2 to about 25 mol %,    -   s is from about 1 to about 15 mol %, and    -   t is from about 15 to about 30 mol %.

A primary polymeric binder comprising recurring units that arerepresented by Structure (I) or (I-A) may contain recurring units otherthan those defined by the noted Structures and such recurring unitswould be readily apparent to a skilled worker in the art. Thus,Structures (I) and (I-A) in their broadest sense are not limited to thedefined recurring units. However, in some embodiments, only therecurring units specifically defined in Structure (I) or (I-A) arepresent.

There may be multiple types of recurring units from any of the definedclasses of recurring units of Structures (Ia) through (Ig) withdifferent substituents. For example, there may be multiple types ofrecurring units of Structure (Ia) with different R¹ groups. Suchmultiplicity of recurring units can also be true for those representedby any of Structures (Ib), (Ic), (Id), (Ie), (If), and (Ig).

Content of the primary polymeric binder in the radiation-sensitivecomposition that forms a radiation-sensitive layer is generally fromabout 10 to about 99% of the total dry weight, and typically from about30 to about 95% of the total dry weight. Many embodiments would includethe primary polymeric binder in an amount of from about 50 to about 90%of the total composition or layer dry weight.

The poly(vinyl acetals) of Structure (I) or (I-A) described herein canbe prepared using known starting materials and reaction conditionsincluding those described in U.S. Pat. No. 6,541,181 (noted above).

For example, acetalization of the polyvinyl alcohols can take placeaccording to known standard methods for example as described in U.S.Pat. No. 4,665,124 (Dhillon et al.), U.S. Pat. No. 4,940,646(Pawlowski), U.S. Pat. No. 5,169,898 (Walls et al.), U.S. Pat. No.5,700,619 (Dwars et al.), and U.S. Pat. No. 5,792,823 (Kim et al.), andin Japanese Kokai 09-328,519 (Yoshinaga).

This acetalization reaction generally requires addition of a stronginorganic or organic catalyst acid. Examples of catalyst acids arehydrochloric acid, sulfuric acid, phosphoric acid, and p-toluenesulfonicacid. Other strong acids are also useful such as perfluoroalkylsulfonicacid and other perfluoro-activated acids. The amount of acid shouldeffectively allow protonation to occur, but will not significantly alterthe final product by causing unwanted hydrolysis of the acetal groups.The reaction temperature of the acetalization depends on the kind ofaldehyde as well as the desired level of substitution. It is between 0°C. and, if applicable, the boiling point of the solvent. Organicsolvents as well as mixtures of water with organic solvents are used forthe reaction. For example, suitable organic solvents are alcohols (suchas methanol, ethanol, n-propanol, n-butanol, and glycol ether), cyclicethers (such as 1,4-dioxane), and dipolar aprotic solvents (such asN,N-dimethylformamide, N-methyl pyrrolidone, or dimethyl sulfoxide). Ifacetalization is carried out in organic solvents or mixtures of organicsolvents with water, the reaction product often remains in solution evenif the starting polyvinyl alcohol was not completely dissolved.Incomplete dissolution of the starting polyvinyl alcohol in organicsolvents is a disadvantage that may lead to irreproducible degree ofconversion and different products. Water or mixtures of organic solventswith water should be used to achieve complete dissolution of polyvinylalcohol and reproducible products as a result of acetalization. Thesequence of the addition of the various acetalization agents is often ofno importance and comparable finished products are obtained fromdifferent preparation sequences. To isolate the finished products as asolid, the polymer solution is introduced into a non-solvent undervigorous stirring, filtered off and dried. Water is especially suitableas a non-solvent for the polymers.

Unwanted hydrolysis of the acetal group achieved by acetalization withhydroxyl-substituted aromatic aldehydes takes place much easier than forthe acetals built from aliphatic or not substituted aromatic aldehydesor from aldehydes containing carboxylic moieties at the same synthesisconditions. The presence of even a small amount of water in the reactionmixture leads to decreased degree of acetalization and incompleteconversion of the aromatic hydroxy aldehyde used. On the other hand, itwas found that in the absence of water, the hydroxy-substituted aromaticaldehydes react with hydroxyl groups of alcohols immediately and withalmost 100% conversion. So, the process of acetalization of polyvinylalcohols by hydroxy-substituted aromatic aldehydes to achieve thedesired polyvinyl acetals according can be carried out different fromthe procedures known in the art. The water can be removed from thereaction mixture during the synthesis by distillation under reducedpressure and replaced with an organic solvent. The remaining water maybe removed by addition to the mixture an organic material readilyreactive with water and as a result of the reaction producing volatilematerials or inert compounds. These materials may be chosen fromcarbonates, orthoesters of carbonic or carboxylic acids, which easilyreact with water, silica-containing compounds, such as diethylcarbonate,trimethyl orthoformate, tetraethyl carbonate, and tetraethyl silicate.The addition of these materials to reaction mixture leads to 100%conversion of the used aldehydes.

Thus, the preparation of a useful poly(vinyl acetal) can begin withdissolving of the starting polyvinyl alcohol in DMSO at 80-90° C., thenthe solution is chilled to 60° C., and the acidic catalyst dissolved inan organic solvent is added. Then the solution of the aliphatic aldehydein the same solvent is added to the solution, the solution is kept for30 minutes at 60° C., and a solution of the aromatic aldehyde and/orcarboxylic substituted aldehyde, or other aldehyde in the same solventis added. Anisole is added to the reaction mixture, and the azeothropicmixture of water with the anisole is removed by distillation and isreplaced by the organic solvent. At this stage, the conversion of thearomatic hydroxy aldehyde reaches 95-98%. The acid in the reactionmixture is neutralized and the mixture is blended with water toprecipitate the polymer that is filtrated, washed with water, and dried.A second way to achieve 100% of conversion of the aromatichydroxyaldehyde to benzal is to add the water removing organic material(for example, a carbonate or orthoformate) after addition of thealdehydes to the reaction mixture.

All acetal groups are 6-membered cyclic acetal groups. The lactonemoiety is derived from the crotonic acid component by dehydration duringthe distillation stage of the reaction.

The poly(vinyl acetal) is generally present in the radiation-sensitivecomposition and the imageable layer of the imageable element generallyin an amount of from about 10 weight % to about 99 weight %, andtypically from about 30 to about 95 weight % based on the total solidsin the composition or layer. Many embodiments would include thepoly(vinyl acetal) in an amount of from about 50 to about 90 weight %based on the total solids.

The poly(vinyl acetal)s described herein generally comprise from about10 weight % to about 100 weight % of the total polymeric binders in theradiation-sensitive composition or imageable layer, and typically fromabout 50 to 100 weight % of the total polymeric binders.

The poly(vinyl acetal)s described herein can be used alone or inadmixture with other alkali soluble polymeric binders, identified hereinas “secondary polymeric binders”. These additional polymeric bindersinclude poly(vinyl acetal)s that are outside the scope of the primarypolymeric binders [that is, not being within Structure (I) or (I-A)],for example, the poly(vinyl acetal)s described in U.S. Pat. Nos.6,255,033 and 6,541,181 (noted above), WO 04/081662 (also noted above),and in copending and commonly assigned U.S. Ser. No. 11/677,599 (filedFebruary, 2007 by Levanon et al.), which publications and copendingapplication are incorporated herein by reference.

The type of the secondary polymeric binder that can be used togetherwith the primary polymeric binder is not particularly restricted. Ingeneral, from a viewpoint of not diminishing the positiveradiation-sensitivity of the imageable element, the secondary polymericbinder is generally an alkali-soluble polymer also.

Other useful secondary polymeric binders include phenolic resins,including novolak resins such as condensation polymers of phenol andformaldehyde, condensation polymers of m-cresol and formaldehyde,condensation polymers of p-cresol and formaldehyde, condensationpolymers of m-/p-mixed cresol and formaldehyde, condensation polymers ofphenol, cresol (m-, p-, or m-/p-mixture) and formaldehyde, andcondensation copolymers of pyrogallol and acetone. Further, copolymersobtained by copolymerizing compound comprising phenol groups in the sidechains can be used. Mixtures of such polymeric binders can also be used.

Novolak resins having a weight average molecular weight of at least1,500 and a number average molecular weight of at least 300 are useful.Generally, the weight average molecular weight is in the range of fromabout 3,000 to about 300,000, the number average molecular weight isfrom about 500 to about 250,000, and the degree of dispersion (weightaverage molecular weight/number average molecular weight) is in therange of from about 1.1 to about 10.

Certain mixtures of the primary polymeric binders described above can beused, including mixtures of one or more poly(vinyl acetals) and one ormore phenolic resins. For example, mixtures of one or more poly(vinylacetals) and one or more novolak or resol (or resole) resins (or bothnovolak and resol resins) can be used.

Examples of other secondary polymeric binders include the followingclasses of polymers having an acidic group in (1) through (5) shownbelow on a main chain and/or side chain (pendant group).

(1) sulfone amide (—SO₂NH—R),

(2) substituted sulfonamido based acid group (hereinafter, referred toas active imido group) [such as —SO₂NHCOR, SO₂NHSO₂R, —CONHSO₂R],

(3) carboxylic acid group (—CO₂H),

(4) sulfonic acid group (—SO₃H), and

(5) phosphoric acid group (—OPO₃H₂).

R in the above-mentioned groups (1)-(5) represents hydrogen or ahydrocarbon group.

Representative secondary polymeric binders having the group (1) sulfoneamide group are for instance, polymers that are constituted of a minimumconstituent unit as a main component derived from a compound having asulfone amide group. Thus, examples of such a compound include acompound having, in a molecule thereof, at least one sulfone amide groupin which at least one hydrogen atom is bound to a nitrogen atom and atleast one polymerizable unsaturated group. Among these compounds arem-aminosulfonylphenyl methacrylate,N-(p-aminosulfonylphenyl)methacrylamide, andN-(p-aminosulfonylphenyl)acrylamide. Thus, a homopolymer or a copolymerof polymerizing monomers having a sulfonamide group such asm-aminosulfonylphenyl methacrylate, N-(p-aminosulfonylphenyl)methacrylamide, or N-(p-aminosulfonylphenyl) acrylamide can be used.

Examples of secondary polymeric binders with group (2) activated imidogroup are polymers comprising recurring units derived from compoundshaving activated imido group as the main constituent component. Examplesof such compounds include polymerizable unsaturated compounds having amoiety defined by the following structural formula.

N-(p-toluenesulfonyl) methacrylamide and N-(p-toluenesulfonyl)acrylamide are examples of such polymerizable compounds.

Secondary polymeric binders having any of the groups (3) through (5)include those readily prepared by reacting ethylenically unsaturatedpolymerizable monomers having the desired acidic groups, or groups thatcan be converted to such acidic groups after polymerization.

Regarding the minimum constituent units having an acidic group that isselected from the (1) through (5), there is no need to use only one kindof acidic group in the polymer, and in some embodiments, it may beuseful to have at least two kinds of acidic groups. Obviously, not everyrecurring unit in the secondary polymeric binder must have one of theacidic groups, but usually at least 10 mol % and typically at least 20mol % comprise the recurring units having one of the noted acidicgroups.

The secondary polymeric binder can have a weight average molecularweight of at least 2,000 and a number average molecular weight of atleast 500. Typically, the weight average molecular weight is from about5,000 to about 300,000, the number average molecular weight is fromabout 800 to about 250,000, and the degree of dispersion (weight averagemolecular weight/number average molecular weight) is from about 1.1 toabout 10.

Mixtures of the secondary polymeric binders may be used with the one ormore primary polymeric binders. The secondary polymeric binder(s) can bepresent in an amount of at least 1 weigh % and up to 50 weight %, andtypically from about 5 to about 30 weight %, based on the dry weight ofthe total polymeric binders in the radiation-sensitive composition orimageable layer.

The radiation-sensitive composition can also include adevelopability-enhancing composition containing one or moredevelopability-enhancing compounds. In some embodiments, such compoundshave a boiling point greater than 300° C. and an evaporation rate < 0.01relative to n-butyl acetate. Most of the useful basicnitrogen-containing organic compounds are liquids at 25° C. Two or moreof these compounds can be used if desired.

Examples of basic nitrogen-containing organic compounds useful in thedevelopability-enhancing compositions areN-(2-hydroxyethyl)-2-pyrrolidone, 1-(2-hydroxyethyl)piperazine,N-phenyldiethanolamine, triethanolamine,2-[bis(2-hydroxyethyl)amino]-2-hydroxymethyl-1.3-propanediol,N,N,N′,N′-tetrakis(2-hydroxyethyl)-ethylenediamine,N,N,N′,N′-tetrakis(2-hydroxypropyl)-ethylenediamine,N,N,N′,N′-tetrakis(2-hydroxypropyl)-ethylenediamine, andhexahydro-1,3,5-tris(2-hydroxyethyl)-s-triazine. The basicnitrogen-containing organic compounds can be obtained from a number ofcommercial sources including BASF (Germany) and Aldrich Chemical Company(Milwaukee, Wis.). Further details about these compounds are provided incopending and commonly assigned U.S. Ser. No. 11/677,599 (noted above)that is incorporated herein by reference. The basic nitrogen-containingorganic compound(s) can be present in the radiation-sensitivecomposition (and imageable layer) in an amount of from about 1 to about30 weight %, and typically from about 3 to about 15 weight %, based onthe total solids of the radiation-sensitive composition or total dryweight of the imageable layer.

It is also possible to use one or more of these basicnitrogen-containing organic compounds in combination with one or moreacidic developability-enhancing compounds, such as carboxylic acids orcyclic acid anhydrides, sulfonic acids, sulfinic acids, alkylsulfuricacids, phosphonic acids, phosphinic acids, phosphonic acid esters,phenols, sulfonamides, or sulfonimides, since such a combination maypermit further improved developing latitude and printing durability.Representative examples of such compounds are provided in [0030] to[0036] of U.S. Patent Application Publication 2005/0214677 (noted above)that is incorporated herein by reference with respect to these aciddevelopability-enhancing compounds. Such acidic developability-enhancingcompounds may be present in an amount of from about 0.1 to about 30weight % based on the total dry weight of the radiation-sensitivecomposition or imageable layer. In some instances, at least two of theseacidic developability-enhancing compounds are used in combination withone or more (such as two) of the basic-nitrogen-containing organiccompounds described above.

In the combinations of the basic and acidic compounds described above,the molar ratio of one or more basic nitrogen-containing organiccompounds to one or more acidic developability-enhancing compounds isgenerally from about 0.1:1 to about 10:1 and more typically from about0.5:1 to about 2:1.

The radiation-sensitive composition can include other optional addendaas described below for the imageable layer.

Imageable Elements

The imageable elements are positive-working imageable elements and thepoly(vinyl acetal)s described herein are generally present as polymericbinders in a single imageable layer of these elements. As noted above,they can be the sole polymeric binders or used in mixture with one ormore secondary polymeric binders.

In general, the imageable elements are formed by suitable application ofa formulation of the radiation-sensitive composition that contains oneor more polymeric binders, a radiation absorbing compound (describedbelow), optionally a developability-enhancing composition, and otheroptional addenda, to a suitable substrate to form an imageable layer.This substrate is usually treated or coated in various ways as describedbelow prior to application of the formulation. For example, thesubstrate can be treated to provide an “interlayer” for improvedadhesion or hydrophilicity, and the imageable layer is applied over theinterlayer.

The substrate generally has a hydrophilic surface, or a surface that ismore hydrophilic than the applied imaging formulation on the imagingside. The substrate comprises a support that can be composed of anymaterial that is conventionally used to prepare imageable elements suchas lithographic printing plates. It is usually in the form of a sheet,film, or foil, and is strong, stable, and flexible and resistant todimensional change under conditions of use so that color records willregister a full-color image. Typically, the support can be anyself-supporting material including polymeric films (such as polyester,polyethylene, polycarbonate, cellulose ester polymer, and polystyrenefilms), glass, ceramics, metal sheets or foils, or stiff papers(including resin-coated and metallized papers), or a lamination of anyof these materials (such as a lamination of an aluminum foil onto apolyester film). Metal supports include sheets or foils of aluminum,copper, zinc, titanium, and alloys thereof.

Polymeric film supports may be modified on one or both surfaces with a“subbing” layer to enhance hydrophilicity, or paper supports may besimilarly coated to enhance planarity. Examples of subbing layermaterials include but are not limited to, alkoxysilanes,amino-propyltriethoxysilanes, glycidioxypropyl-triethoxysilanes, andepoxy functional polymers, as well as conventional hydrophilic subbingmaterials used in silver halide photographic films (such as gelatin andother naturally occurring and synthetic hydrophilic colloids and vinylpolymers including vinylidene chloride copolymers).

One substrate is composed of an aluminum support that may be coated ortreated using techniques known in the art, including physical graining,electrochemical graining and chemical graining, followed by anodizing.The aluminum sheet is mechanically or electrochemically grained andanodized using phosphoric acid or sulfuric acid and conventionalprocedures.

An optional interlayer may be formed by treatment of the aluminumsupport with, for example, a silicate, dextrine, calcium zirconiumfluoride, hexafluorosilicic acid, phosphate/sodium fluoride, poly(vinylphosphonic acid) (PVPA), vinyl phosphonic acid copolymer, poly(acrylicacid), or acrylic acid copolymer solution, or an alkali salt of acondensed aryl sulfonic acid as described in GB 2,098,627 and JapaneseKokai 57-195697A (both Herting et al.). The grained and anodizedaluminum support can be treated with poly(acrylic acid) using knownprocedures to improve surface hydrophilicity.

The thickness of the substrate can be varied but should be sufficient tosustain the wear from printing and thin enough to wrap around a printingform. Some embodiments include a treated aluminum foil having athickness of from about 100 to about 600 μm.

The backside (non-imaging side) of the substrate may be coated withantistatic agents and/or slipping layers or a matte layer to improvehandling and “feel” of the imageable element.

The substrate can also be a cylindrical surface having theradiation-sensitive composition applied thereon, and thus be an integralpart of the printing press. The use of such imaged cylinders isdescribed for example in U.S. Pat. No. 5,713,287 (Gelbart).

The imageable layer typically also comprises one or more radiationabsorbing compounds. While these compounds can be sensitive to anysuitable energy form (for example, UV, visible, and IR radiation) fromabout 150 to about 1500 nm, they are typically sensitive to infraredradiation and thus, the radiation absorbing compounds are known asinfrared radiation absorbing compounds (“IR absorbing compounds”) thatgenerally absorb radiation from about 600 to about 1400 nm and typicallyfrom about 700 to about 1200 nm. The imageable layer is generally theoutermost layer in the imageable element.

Examples of suitable IR dyes include but are not limited to, azo dyes,squarylium dyes, croconate dyes, triarylamine dyes, thioazolium dyes,indolium dyes, oxonol dyes, oxazolium dyes, cyanine dyes, merocyaninedyes, phthalocyanine dyes, indocyanine dyes, indotricarbocyanine dyes,hemicyanine dyes, streptocyanine dyes, oxatricarbocyanine dyes,thiocyanine dyes, thiatricarbocyanine dyes, merocyanine dyes,cryptocyanine dyes, naphthalocyanine dyes, polyaniline dyes, polypyrroledyes, polythiophene dyes, chalcogenopyryloarylidene andbi(chalcogenopyrylo)-polymethine dyes, oxyindolizine dyes, pyryliumdyes, pyrazoline azo dyes, oxazine dyes, naphthoquinone dyes,anthraquinone dyes, quinoneimine dyes, methine dyes, arylmethine dyes,polymethine dyes, squarine dyes, oxazole dyes, croconine dyes, porphyrindyes, and any substituted or ionic form of the preceding dye classes.Suitable dyes are described for example, in U.S. Pat. No. 4,973,572(DeBoer), U.S. Pat. No. 5,208,135 (Patel et al.), U.S. Pat. No.5,244,771 (Jandrue Sr. et al.), and U.S. Pat. No. 5,401,618 (Chapman etal.), and EP 0 823 327A1 (Nagasaka et al.).

Cyanine dyes having an anionic chromophore are also useful. For example,the cyanine dye may have a chromophore having two heterocyclic groups.In another embodiment, the cyanine dye may have from about two sulfonicacid groups, such as two sulfonic acid groups and two indolenine groups.Useful IR-sensitive cyanine dyes of this type are described for examplein U.S. Patent Application Publication 2005-0130059 (Tao).

A general description of a useful class of suitable cyanine dyes isshown by the formula in [0026] of WO 2004/101280 (Munnelly et al.).

In addition to low molecular weight IR-absorbing dyes, IR dye moietiesbonded to polymers can be used. Moreover, IR dye cations can be used aswell, that is, the cation is the IR absorbing portion of the dye saltthat ionically interacts with a polymer comprising carboxy, sulfo,phospho, or phosphono groups in the side chains.

Near infrared absorbing cyanine dyes are also useful and are describedfor example in U.S. Pat. No. 6,309,792 (Hauck et al.), U.S. Pat. No.6,264,920 (Achilefu et al.), U.S. Pat. No. 6,153,356 (Urano et al.), andU.S. Pat. No. 5,496,903 (Watanate et al.). Suitable dyes may be formedusing conventional methods and starting materials or obtained fromvarious commercial sources including American Dye Source (Baie D'Urfe,Quebec, Canada) and FEW Chemicals (Germany). Other useful dyes for nearinfrared diode laser beams are described, for example, in U.S. Pat. No.4,973,572 (noted above). The following IR dyes, as well as those used inthe Examples below, are representative of useful radiation absorbingcompounds and are not meant to be limiting in any way:

Same as above but with C₃F₇CO₂ ⁻ as the anion.

Useful IR absorbing compounds can also be pigments including carbonblacks such as carbon blacks that are surface-functionalized withsolubilizing groups are well known in the art. Carbon blacks that aregrafted to hydrophilic, nonionic polymers, such as FX-GE-003(manufactured by Nippon Shokubai), or which are surface-functionalizedwith anionic groups, such as CABO-JET® 200 or CAB-O-JET® 300(manufactured by the Cabot Corporation) are also useful. Other usefulpigments include, but are not limited to, Heliogen Green, NigrosineBase, iron (III) oxides, manganese oxide, Prussian Blue, and Paris Blue.The size of the pigment particles should not be more than the thicknessof the imageable layer and preferably the pigment particle size will beless than half the thickness of the imageable layer.

In the imageable elements, the radiation absorbing compound is generallypresent at a dry coverage of from about 0.1 to about 20 weight %, or itis an IR dye that is present in an amount of from about 0.5 to about 5weight %. Alternatively, the amount can be defined by an absorbance inthe range of from about 0.05 to about 3, or from about 0.1 to about 1.5,in the dry film as measured by reflectance UV-visible spectrophotometry.The particular amount needed for this purpose would be readily apparentto one skilled in the art, depending upon the specific compound used.

Alternatively, the radiation absorbing compounds may be included in aseparate layer that is in thermal contact with the imageable layer.Thus, during imaging, the action of the radiation absorbing compound inthe separate layer can be transferred to the imageable layer without thecompound originally being incorporated into it.

The imageable layer (and radiation-sensitive composition) can alsoinclude one or more additional compounds that are colorant dyes.Colorant dyes that are soluble in an alkaline developer are useful.Useful polar groups for colorant dyes include but are not limited to,ether groups, amine groups, azo groups, nitro groups, ferroceniumgroups, sulfoxide groups, sulfone groups, diazo groups, diazoniumgroups, keto groups, sulfonic acid ester groups, phosphate ester groups,triarylmethane groups, onium groups (such as sulfonium, iodonium, andphosphonium groups), groups in which a nitrogen atom is incorporatedinto a heterocyclic ring, and groups that contain a positively chargedatom (such as quaternized ammonium group). Compounds that contain apositively-charged nitrogen atom useful as colorant dyes include, forexample, tetraalkyl ammonium compounds and quaternized heterocycliccompounds such as quinolinium compounds, benzothiazolium compounds,pyridinium compounds, and imidazolium compounds. Further details andrepresentative compounds useful as dissolution inhibitors are describedfor example in U.S. Pat. No. 6,294,311 (noted above). Useful colorantdyes include triarylmethane dyes such as ethyl violet, crystal violet,malachite green, brilliant green, Victoria blue B, Victoria blue R, andVictoria pure blue BO, BASONYL® Violet 610 and D11 (PCAS, Longjumeau,France). These compounds can act as contrast dyes that distinguish thenon-exposed (non-imaged) regions from the exposed (imaged) regions inthe developed imageable element.

When a colorant dye is present in the imageable layer, its amount canvary widely, but generally it is present in an amount of from about 0.5weight % to about 30 weight %.

The imageable layer (and radiation-sensitive composition) can furtherinclude a variety of additives including dispersing agents, humectants,biocides, plasticizers, surfactants for coatability or other properties,viscosity builders, fillers and extenders, pH adjusters, drying agents,defoamers, preservatives, antioxidants, development aids, rheologymodifiers or combinations thereof, or any other addenda commonly used inthe lithographic art, in conventional amounts.

The positive-working imageable element can be prepared by applying theimageable layer formulation over the surface of the substrate (and anyother hydrophilic layers provided thereon) using conventional coating orlamination methods. Thus, the formulation can be applied by dispersingor dissolving the desired ingredients in a suitable coating solvent, andthe resulting formulation is applied to the substrate using suitableequipment and procedures, such as spin coating, knife coating, gravurecoating, die coating, slot coating, bar coating, wire rod coating,roller coating, or extrusion hopper coating. The formulation can also beapplied by spraying onto a suitable support (such as an on-pressprinting cylinder).

The coating weight for the imageable layer is from about 0.5 to about2.5 g/m² and typically from about 1 to about 2 g/m².

The selection of solvents used to coat the layer formulation(s) dependsupon the nature of the polymeric binders and other polymeric materialsand non-polymeric components in the formulations. Generally, theimageable layer formulation is coated out of acetone, methyl ethylketone, or another ketone, tetrahydrofuran, 1-methoxy-2-propanol,N-methyl pyrrolidone, 1-methoxy-2-propyl acetate, γ-butyrolactone, andmixtures thereof using conditions and techniques well known in the art.

Alternatively, the layer(s) may be applied by conventional extrusioncoating methods from melt mixtures of the respective layer compositions.Typically, such melt mixtures contain no volatile organic solvents.

Intermediate drying steps may be used between applications of thevarious layer formulations to remove solvent(s) before coating otherformulations. Drying steps may also help in preventing the mixing of thevarious layers.

Representative methods for preparing positive-working imageable elementsare described below in the examples.

After the imageable layer formulation is dried on the substrate (thatis, the coating is self-supporting and dry to the touch), the elementcan be heat treated at from about 40 to about 90° C. (typically at fromabout 50 to about 70° C.) for at least 4 hours and preferably at least20 hours, or for at least 24 hours. The maximum heat treatment time canbe several days, but the optimal time and temperature for the heattreatment can be readily determined by routine experimentation. Thisheat treatment can also be known as a “conditioning” step. Suchtreatments are described for example, in EP 823,327 (Nagaska et al.) andEP 1,024,958 (McCullough et al.).

It may also be desirable that during the heat treatment, the imageableelement is wrapped or encased in a water-impermeable sheet material torepresent an effective barrier to moisture removal from the precursor.This sheet material is sufficiently flexible to conform closely to theshape of the imageable element (or stack thereof) and is generally inclose contact with the imageable element (or stack thereof). Forexample, the water-impermeable sheet material is sealed around the edgesof the imageable element or stack thereof. Such water-impermeable sheetmaterials include polymeric films or metal foils that are sealed aroundthe edges of imageable element or stack thereof.

Alternatively, the heat treatment (or conditioning) of the imageableelement (or stack thereof) is carried out in an environment in whichrelative humidity is controlled to from about 25%, or from about 30%.Relative humidity is defined as the amount of water vapor present in airexpressed as a percentage of the amount of water required for saturationat a given temperature.

Usually, at least 5 and up to 100 imageable elements are heat treated atthe same time. More commonly, such a stack includes at least 500imageable elements.

In may be difficult to achieve good wrapping at the top and bottom ofsuch a stack using the water-impermeable sheet material and in suchinstances, it may be desirable to use “dummy” or reject elements inthose regions of the stack. Thus, the heat-treated (or “conditioned”)stack may include at least 100 useful imageable elements in combinationwith dummy or reject elements. These dummy or reject elements also serveto protect the useful elements from damage caused by the wrapping orsealing process.

Alternatively, the imageable element(s) may be heat treated in the formof a coil and then cut into individual elements at a later time. Suchcoils can include at least 1000 m² of imageable surface and moretypically at least 3000 m² of imageable surface.

Adjacent coils or “spirals” or a coil, or strata of a stack may, ifdesired, be separated by interleaving materials, for example, papers ortissues that may be sized with plastics or resins (such as polythene).

Imaging and Development

The imageable elements of this invention can have any useful formincluding, but not limited to, printing plate precursors, printingcylinders, printing sleeves and printing tapes (including flexibleprinting webs). For example, the imageable members are lithographicprinting plate precursors for forming lithographic printing plates.

Printing plate precursors can be of any useful size and shape (forexample, square or rectangular) having the requisite imageable layerdisposed on a suitable substrate. Printing cylinders and sleeves areknown as rotary printing members having the substrate and imageablelayer in a cylindrical form. Hollow or solid metal cores can be used assubstrates for printing sleeves.

During use, the imageable elements are exposed to a suitable source ofradiation such as UV, visible light, or infrared radiation, dependingupon the radiation absorbing compound present in the radiation-sensitivecomposition, at a wavelength of from about 150 to about 1500 nm. Formost embodiments, imaging is carried out using an infrared laser at awavelength of from about 700 to about 1200 nm. The laser used to exposethe imaging member is can be a diode laser, because of the reliabilityand low maintenance of diode laser systems, but other lasers such as gasor solid-state lasers may also be used. The combination of power,intensity and exposure time for laser imaging would be readily apparentto one skilled in the art. Presently, high performance lasers or laserdiodes used in commercially available imagesetters emit infraredradiation at a wavelength of from about 800 to about 850 nm or fromabout 1060 to about 1120 nm.

The imaging apparatus can function solely as a platesetter or it can beincorporated directly into a lithographic printing press. In the lattercase, printing may commence immediately after imaging, thereby reducingpress set-up time considerably. The imaging apparatus can be configuredas a flatbed recorder or as a drum recorder, with the imageable membermounted to the interior or exterior cylindrical surface of the drum. Auseful imaging apparatus is available as models of Creo Trendsetter®imagesetters available from Eastman Kodak Company (Burnaby, BritishColumbia, Canada) that contain laser diodes that emit near infraredradiation at a wavelength of about 830 nm. Other suitable imagingsources include the Crescent 42T Platesetter that operates at awavelength of 1064 nm (available from Gerber Scientific, Chicago, Ill.)and the Screen PlateRite 4300 series or 8600 series platesetter(available from Screen, Chicago, Ill.). Additional useful sources ofradiation include direct imaging presses that can be used to image anelement while it is attached to the printing plate cylinder. An exampleof a suitable direct imaging printing press includes the HeidelbergSM74-DI press (available from Heidelberg, Dayton, Ohio).

IR Imaging speeds may be from about 30 to about 1500 mJ/cm² or fromabout 40 to about 200 mJ/cm².

While laser imaging is usually practiced, imaging can be provided by anyother means that provides thermal energy in an imagewise fashion. Forexample, imaging can be accomplished using a thermoresistive head(thermal printing head) in what is known as “thermal printing”,described for example in U.S. Pat. No. 5,488,025 (Martin et al.).Thermal print heads are commercially available (for example, as FujitsuThermal Head FTP-040 MCS001 and TDK Thermal Head F415 HH7-1089).

Imaging is generally carried out using direct digital imaging. The imagesignals are stored as a bitmap data file on a computer. Such data filesmay be generated by a raster image processor (RIP) or other suitablemeans. The bitmaps are constructed to define the hue of the color aswell as screen frequencies and angles.

Imaging of the imageable element produces an imaged element thatcomprises a latent image of imaged (exposed) and non-imaged(non-exposed) regions. Developing the imaged element with a suitabledeveloper removes the exposed regions of the imageable layer and anylayers underneath it, and exposing the hydrophilic surface of thesubstrate. Thus, such imageable elements are “positive-working” (forexample, “positive-working” lithographic printing plate precursors).

Thus, development is carried out for a time sufficient to remove theimaged (exposed) regions of the imageable layer, but not long enough toremove the non-imaged (non-exposed) regions of the imageable layer. Theimaged (exposed) regions of the imageable layer are described as being“soluble” or “removable” in the developer because they are removed,dissolved, or dispersed within the developer more readily than thenon-imaged (non-exposed) regions of the imageable layer. Thus, the term“soluble” also means “dispersible”.

The imaged elements are generally developed using conventionalprocessing conditions. Both aqueous alkaline developers and organicsolvent-containing developers can be used. In most embodiments of themethod of this invention, the higher pH aqueous alkaline developers thatare commonly used to process positive-working imaged elements are used.

Such aqueous alkaline developers generally have a pH of at least 9 andpreferably at least 11. Useful alkaline aqueous developers include 3000Developer, 9000 Developer, GOLDSTAR Developer, GOLDSTAR Plus Developer,GOLDSTAR Premium Developer, GREENSTAR Developer, ThermalPro Developer,PROTHERM Developer, MX1813 Developer, T-189-8 Developer (noted below inthe Examples), and MX1710 Developer (all available from Eastman KodakCompany), as well as Fuji HDP7 Developer (Fuji Photo) and Energy CTPDeveloper (Agfa). These compositions also generally include surfactants,chelating agents (such as salts of ethylenediaminetetraacetic acid), andvarious alkaline agents (such as inorganic metasilicates, organicmetasilicates, hydroxides, and bicarbonates).

It may also be possible to use developers that are commonly used toprocess negative-working imaged elements. Such developers are generallysingle-phase solutions containing one or more organic solvents that aremiscible with water. Useful organic solvents the reaction products ofphenol with ethylene oxide and propylene oxide [such as ethylene glycolphenyl ether (phenoxyethanol)], benzyl alcohol, esters of ethyleneglycol and of propylene glycol with acids having 6 or less carbon atoms,and ethers of ethylene glycol, diethylene glycol, and of propyleneglycol with alkyl groups having 6 or less carbon atoms, such asmethoxyethanol and 2-butoxyethanol. The organic solvent(s) is generallypresent in an amount of from about 0.5 to about 15% based on totaldeveloper weight. Such developers can be neutral, alkaline, or slightlyacidic in pH. Most of these developers are alkaline in pH, for exampleup to 11.

Representative organic solvent-containing developers include ND-1Developer, 955 Developer, “2 in 1” Developer, and 956 Developer(available from Eastman Kodak Company).

Generally, the developer is applied to the imaged element by rubbing orwiping it with an applicator containing the developer. Alternatively,the imaged element can be brushed with the developer or the developermay be applied by spraying the element with sufficient force to removethe exposed regions. Still again, the imaged element can be immersed inthe developer. In all instances, a developed image is produced in alithographic printing plate having excellent resistance to press roomchemicals.

Following development, the imaged element can be rinsed with water anddried in a suitable fashion. The dried element can also be treated witha conventional gumming solution (preferably gum arabic).

The imaged and developed element can also be baked in a post-exposurebake operation that can be carried out to increase run length of theresulting imaged element. Baking can be carried out, for example at fromabout 220° C. to about 240° C. for from about 7 to about 10 minutes, orat about 120° C. for about 30 minutes.

Printing can be carried out by applying a lithographic ink and fountainsolution to the printing surface of the imaged element. The ink is takenup by the non-imaged (non-exposed or non-removed) regions of theimageable layer and the fountain solution is taken up by the hydrophilicsurface of the substrate revealed by the imaging and developmentprocess. The ink is then transferred to a suitable receiving material(such as cloth, paper, metal, glass, or plastic) to provide a desiredimpression of the image thereon. If desired, an intermediate “blanket”roller can be used to transfer the ink from the imaged member to thereceiving material. The imaged members can be cleaned betweenimpressions, if desired, using conventional cleaning means andchemicals.

The following examples are presented as a means to illustrate thepractice of this invention but the invention is not intended to belimited thereby.

EXAMPLES

The following components were used in the preparation and use of theexamples. Unless otherwise indicated, the components are available fromAldrich Chemical Company (Milwaukee, Wis.):

BC represents butyl cellusolve (ethylene glycol butyl ether).

BF-03 represents a poly(vinyl alcohol), 98% hydrolyzed (Mw=15,000) thatwas obtained from Chang Chun Petrochemical Co. Ltd. (Taiwan).

Crystal Violet (C.I. 42555) is Basic Violet 3 (λ_(max)=588 nm).

DAA represents diacetone alcohol (4-hydroxy-4-methyl-2-pentanone).

DMFA represents N,N-dimethylformamide.

DMSO represents dimethylsulfoxide.

HEP represents 1-(2-hydroxyethyl)-2-pyrrolidone.

MC represents methyl cellulose.

MEK represents methyl ethyl ketone.

Mowilith® MCT5 is a copolymer of vinyl acetate and crotonic acid(Mw=36,000) (95:5 molar ratio), acid value of 35-45 mg KOH/g that wasobtained from Synthomer Ltd. (Harlow, UK).

MSA represents methanesulfonic acid (99%).

NMP represents N-methyl pyrrolidone.

PG represents phloroglucinol.

PGide represents phloroglucide.

PM represents 1-methoxy-2-propanol.

PVA-co-crotonic acid represents a copolymer of poly(vinylacetate-co-crotonic acid) (90:10 mole ratio), acid value 62-70 mg KOH/g.

S 0094 is an IR dye (λ_(max)=813 nm) that was obtained from FEWChemicals (Germany).

S 0451 is an IR dye (λ_(max)=775 nm) that was obtained from FEWChemicals (Germany).

Sudan Black B is a neutral diazo dye (C.U. 26150).

Synthomer MCTS is a copolymer of vinyl acetate and crotonic acid(Mw=36,000), acid value 35-45 mg KOH/g that was obtained from SynthomerLtd. (Harlow, UK).

T-189-8 is an aqueous alkaline positive developer that was obtained fromEastman Kodak Company (Rochester, N.Y.).

TEA represents triethanolamine.

UV Wash is a lithographic blanket and roller wash that was obtained fromVarn Chemical Products (Irlam, Greater Manchester, UK).

Preparation of Polymer A:

Polymer A was prepared as described in copending and commonly assignedU.S. Ser. No. 11/677,599 (filed Feb. 22, 2007 by Levanon et al.).

BF-03 (50 g) was added to reaction vessel fitted with a water-cooledcondenser, a dropping funnel, and thermometer, and containing DMSO (200g). With continual stirring, the mixture was heated for 30 minutes at80° C. until it became a clear solution. The temperature was thenadjusted at 60° C. and MSA (2.7g) in DMSO (50 g) was added. Over 15minutes, a solution of butyraldehyde (10.4 g) was added to the reactionmixture and it was kept for 1 hour at 55-60° C. Then,2-hydroxybenzaldehyde (salicylic aldehyde, 39 g) in DMSO (100 g) wasadded to the reaction mixture. The reaction mixture was then dilutedwith anisole (350 g) and vacuum distillation was started. Theanisole:water azeotrope was distilled out from the reaction mixture(less than 0.1% of water remained in the solution). The reaction mixturewas chilled to room temperature and was neutralized with TEA (8 g)dissolved in DMSO (30 g), then blended with 6 kg of water. Theprecipitated polymer was washed with water, filtered and dried in vacuumfor 24 hours at 50° C. to obtain 86 g of dry Polymer A.

Preparation of Polymer B:

Polymer B was prepared like Polymer A except that instead of a mixtureof butyraldehyde and salicylic acid, only salicylic aldehyde (54 g) wasused. About 85.0 g of Polymer B were obtained.

Preparation of Polymer C:

Polymer C was prepared like Polymer B except that instead of salicylicaldehyde, a mixture of salicylic aldehyde (13.6 g) and2-hydroxynaphthoic aldehyde (43.6 g) was used. About 85.6 g of Polymer Cwere obtained.

Preparation of Polymer D:

Poly(vinyl acetate-co-crotonic acid) (100 g) was dissolved in methanol(1000 ml). A sodium methylate solution (2 grams of sodium and 40 ml ofmethanol) was added drop-wise to the polymer solution. The reactionmixture was refluxed for 30 minutes and the precipitated polymerparticles were filtered off. Upon washing with methanol, the polymer wasdried. The procedure described for Polymer B was used except thatinstead of BF-03 polyvinyl alcohol, 50 g of the precipitated polymerparticles were used and MSA (5.5 g) was added. About 75 g of Polymer Dwere obtained.

Preparation of Polymer E:

The procedure used to prepare Polymer D was repeated except that insteadof poly(vinyl acetate-co-crotonic acid), Mowilith® MCT5 (100 g) wasused. About 75 grams of Polymer E were obtained.

Preparation of Polymer F:

The procedure used to prepare Polymer D was repeated except that insteadof salicylic aldehyde, a mixture of salicylic aldehyde (23 g) and2-hydroxynaphthoic aldehyde (27 g) was used. About 78.5 g of Polymer Fwere obtained.

Preparation of Polymer G:

Polymer C was prepared like Polymer B except that instead of salicylicaldehyde, a mixture of salicylic aldehyde (23.6 g), 2-hydroxynaphthoicaldehyde (28.4 g) and 2-formyl-phenoxyacetic acid (8 g) was used. About88.2 g of Polymer G were obtained.

Comparative Example 1:

An imageable element outside of the present invention was prepared inthe following manner. A radiation-sensitive composition was preparedusing the following components:

Polymer A 11.5 g Crystal Violet 0.25 g S 0094 IR Dye 0.125 g  S 0451 IRDye 0.225 g  Sudan Black B 0.125 g  PG 0.25 g PM   45 g MEK   34 g NMP 8.5 g

The composition was filtered and applied to an electrochemicallyroughened and anodized aluminum substrate that had been subjected to anafter treatment using an aqueous solution of poly(vinyl phosphonic acid)by means of common methods and the resulting imageable layer coating isdried for 2.5 minutes at 100° C. in Glunz&Jensen “Unigraph Quartz” oven.The weight of each imageable layer was about 1.5 g/m².

The resulting imageable element was exposed on a CREO Lotem 400 Quantumimager in a range of energies 40 mJ/cm² to 120 mJ/cm² and developed at21° C. in a Glunz&Jensen “InterPlater 85HD” processor using the T189-8developer. The resulting printing plate was evaluated for sensitivity(clearing point: the lowest imaging energy at which the exposed regionswere completely removed by the developer at a given temperature andtime), solvent resistance, bake ability, and on-press run length. Theresults are shown in the following TABLE I below.

Invention Example 1

An imageable element of the present invention was prepared in thefollowing manner. A radiation-sensitive composition was prepared usingthe following components:

Polymer B 10.8 g Crystal Violet 0.25 g S 0094 IR Dye 0.125 g  S 0451 IRDye 0.225 g  Sudan Black B 0.125 g  PG   1 g PM 43.8 g MEK   35 g NMP8.75 g

The composition was coated to provide an imageable layer and dried toprovide an imageable element that was imaged, developed, and evaluatedas described in Comparative Example 1. The results are shown in TABLE Ibelow.

Invention Example 2

Another imageable element of the present invention was prepared in thefollowing manner. A radiation-sensitive composition was prepared usingthe following components:

Polymer C 10.8 g Crystal Violet 0.25 g S 0094 IR Dye 0.125 g  S 0451 IRDye 0.225 g  Sudan Black B 0.125 g  PG   1 g MC 64.7 g MEK 21.6 g NMP1.25 g

The composition was coated to provide an imageable layer and dried toprovide an imageable element that was imaged, developed, and evaluatedfor sensitivity and solvent resistance as described in ComparativeExample 1. The results are shown in TABLE I below.

Invention Example 3

An imageable element of the present invention was prepared in thefollowing manner. A radiation-sensitive composition was prepared usingthe following components:

Polymer D 10.8 g Crystal Violet 0.25 g S 0094 IR Dye 0.125 g  S 0451 IRDye 0.225 g  Sudan Black B 0.125 g  PG   1 g MC 64.7 g MEK 21.6 g NMP1.25 g

The composition was coated to provide an imageable layer and dried toprovide an imageable element that was imaged, developed, and evaluatedfor sensitivity and solvent resistance as described in ComparativeExample 1. The results are shown in TABLE I below.

Invention Examples 4 and 5

An imageable element was prepared in Example 4 like that of

Example 3 except that Polymer E was used instead of Polymer D.Similarly, an imageable element was prepared in Example 5 like that ofExample 2 except that Polymer F was used instead of Polymer C. Theresults are shown in TABLE I below.

Invention Example 6

An imageable element was prepared in Example 6 like that of ComparativeExample 1 except that Polymer G was used instead of Polymer A; andinstead of 0.5 g of PG was used 0.5 g of PGide. The results are shown inTABLE I below

Comparative Examples 2 & 3

Two commercial positive-working printing plate precursors were comparedto the imageable elements of the present invention. These commercialelements were a Kodak Sword Ultra Thermal Printing Plate that isavailable from

Kodak Polychrome Graphics, a subsidiary of Eastman Kodak Company(Norwalk, Conn.), and Fuji Photo's LH-PI printing plate. The Kodak SwordUltra Thermal Printing Plate comprises a single imageable layer thatcontains a predominant polymeric binder that is outside the scope of thepresent invention. Fuji Photo's LH-PI printing plate has a singleimageable layer that is also outside the scope of the present invention.

The elements of Invention Examples 1-6 and Comparative Examples 1-3 wereevaluated in the following tests:

Resistance to UV Wash Test 1: Drops of the Varn UV Wash were placed onthe imaged and developed printing plates at 1 minute intervals up to 4minutes, and then the drops were removed with a cloth. The amount ofremoved printing layer was estimated.

Resistance to UV Wash Test 2: Drops of mixtures of diacetone alcohol(DAA) and water at different ratios were placed on the imaged anddeveloped printing plates at 1 minute intervals up to 4 minutes, andthen the drops were removed with a cloth. The amount of removed printinglayer was estimated.

Resistance to Alcohol-Sub Fountain Solution: Drops of mixtures of2-butoxyethanol (BC) and water at different ratios were placed on theimaged and developed printing plates at 1 minute intervals up to 4minutes, and then the drops were removed with a cloth. The amount ofremoved printing layer was estimated.

The results of these tests are shown in the following TABLE I.

TABLE I SOLVENT RESISTANCE Resistance to Alcohol- Fountain SolutionResistance to UV Wash SENSITIVITY BC:H₂O (4:1) DAA:H₂0 (4:1) UV Wash(Varn) EXAMPLE POLYMER (mJ/cm²) 1 min 4 min 1 min 4 min 1 min 4 minComparative 1 A 50 * * * * * * Invention 1 B 50 * * * * 14%  63%Invention 2 C 50  3% 23% 0 10% 0 13% Invention 3 D 60 20% * 13.5%   68%2% 28% Invention 4 E 60 * * 37% * 11%  65% Invention 5 F 70 0 2.5%  014% 0  7% Invention 6 G 60 0 0 0 3.2%  0 3.7%  Comparative 2 14% 19% 15%38% 8% 12% (Kodak SWORD ULTRA) Comparative 3 0  1% 28% 70% 1% 1.2% (Fuji LH-PI) * Coating dissolved or almost dissolved.

The results in TABLE I show that the compositions containing the primarypoly(vinyl acetals) within the scope of this invention provide imageableelements with excellent solvent resistance to a broad range of presschemicals and high sensitivity when imaged in digital imaging device at700-1000 nm.

The imaged elements of Invention Examples 1-6 were baked after exposurein a Wisconsin SPC-HD 34/125 oven at 260° C. at speeds of 0.5 m/min. to1.0 m/min. DMFA was then applied on each element surface for 5 minutesand wiped with a cloth. The conditions when no coating removal wasobserved considered as full baking These results are presented in TABLEII.

TABLE II EXAMPLE 0.5 m/minute 1 m/minute Comparative 1 Fully bakedInvention 1 Fully baked Invention 2 Fully baked Invention 3 Fully bakedInvention 4 Fully baked Invention 5 Fully baked Invention 6 Fully baked

The results in TABLE II show that the compositions containing thepoly(vinyl acetals) according to this invention provide imageableelements with highly bakeable imageable layer coatings.

The invention has been described in detail with particular reference tocertain preferred embodiments thereof, but it will be understood thatvariations and modifications can be effected within the spirit and scopeof the invention.

1. A positive-working imageable element comprising a substrate havingthereon an imageable layer comprising a radiation-sensitive compositioncomprising: a. an alkaline soluble polymeric binder, and b. a radiationabsorbing compound, the alkaline soluble polymeric binder being apolyvinyl acetal) comprising recurring units that are represented by thefollowing Structures (Id) and (Ie):

wherein R and R′ are independently hydrogen or a substituted orunsubstituted alkyl, substituted or unsubstituted cycloalkyl, or halogroup, and R⁷ is the following group:

wherein X is a direct single bond or a —O—CH₂— group, theradiation-sensitive composition further comprising adevelopability-enhancing composition.
 2. The element of claim 1 whereinthe alkaline soluble polymeric binder also comprises recurring unitsrepresented by the following Structures (Ia) and (Ib):

wherein R and R′ are as defined above, R¹ is a substituted orunsubstituted phenol, substituted or unsubstituted naphthol, orsubstituted or unsubstituted anthracenol group, and R² is a substitutedor unsubstituted naphthol but is different from R¹.
 3. The element ofclaim 1 wherein the alkaline soluble polymeric binder further comprisesrecurring units that are represented by one or more of the followingStructures (Ic), (If), and (Ig):

wherein R and R′ are as defined above, R³ is a substituted orunsubstituted alkynyl group, or a substituted or unsubstituted phenylgroup, R⁴ is an —O—C(═O)—R⁵ group wherein R⁵ is a substituted orunsubstituted alkyl or substituted or unsubstituted aryl group, R⁶ is ahydroxy group,.
 4. The element of claim 3 wherein the recurring unitsrepresented by Structures (Ia), (Ib), (Ic), (Id), (Ie), (If), and (Ig)are present in the polymeric binder in the following amounts: at least20 mol % of recurring units represented by Structure (Ia), at least 10mol % of recurring units represented by Structure (lb), from 2 to 10 mol% of recurring units represented by Structure (Ic), from 2 to 25 mol %of recurring units represented by both of Structures (Id) and (Ie) withthe amounts being the same or different, from 1 to 15 mol % of recurringunits represented by Structure (If), and from 15 to 30 mol % ofrecurring units represented by Structure (Ig).
 5. The element of claim 2wherein the amount of recurring units represented by Structures (Ia) and(Ib) is less than or equal to 75 mol %.
 6. The element of claim 1wherein the radiation absorbing compound is an infrared radiationabsorbing compound.
 7. The element of claim 1 further comprising analkaline soluble phenolic resin or a poly(vinyl acetal) not havingrecurring units represented by Structures (Id) and (Ie).
 8. The elementof claim 1 wherein the developability-enhancing composition comprisesone or more basic nitrogen-containing organic compounds, one or moreacidic developability-enhancing compounds, or one or more of both thebasic nitrogen-containing organic compounds and the acidicdevelopability-enhancing compounds.
 9. The element of claim 8 whereinthe one or more basic nitrogen-containing organic compounds are one ormore of N-(2-hydroxyethyl)-2-pyrrolidone, 1-(2-hydroxyethyl)piperazine,N -phenyldiethanolamine, triethanolamine,2-[bis(2-hydroxyethyl)amino]-2-hydroxymethyl-1.3-propanediol,N,N,N′,N′-tetrakis(2-hydroxyethyl) -ethylenediamine,N,N,N′,N′-tetrakis(2-hydroxypropyl)-ethylenediamine,N,N,N′N′-tetrakis(2-hydroxyethyl)adipamide, andhexahydro-1,3,5-tris(2-hydroxyethyl)-s-triazine, and the one or moreacidic developability-enhancing compounds are one or more carboxylicacids or cyclic acid anhydrides, sulfonic acids, sulfinic acids,alkylsulfuric acids, phosphonic acids, phosphinic acids, phosphonic acidesters, phenols, sulfonamides, or sulfonamides.
 10. The element of claim1 wherein the alkaline soluble polymeric binder is represented by thefollowing Structure (I-A):-(A)_(m)-(B)_(n)-(C)_(p)-(D)_(q)-(E)_(r)-(F)_(s)-(G)_(t)-  (I-A)wherein: A represents recurring units represented by the followingStructure (Ia):

B represents recurring units represented by the following Structure(Ib):

C represents recurring units represented by the following Structure(Ic):

D represents recurring units represented by the following Structure(Id):

E represents recurring units represented by the following Structure(Ie):

F represents recurring units represented by the following Structure(If):

G represents recurring units represented by the following Structure(Ig):

wherein R and R′ are independently hydrogen or a substituted orunsubstituted alkyl, substituted or unsubstituted cycloalkyl, or halogroup, R¹ is a substituted or unsubstituted phenol, substituted orunsubstituted naphthol, or substituted or unsubstituted anthracenolgroup, R² is a substituted or unsubstituted naphthol but is differentfrom R¹, R³ is a substituted or unsubstituted alkynyl group, or asubstituted or unsubstituted phenyl group, R⁴ is an —O—C(═O)—R⁵ groupwherein R⁵ is a substituted or unsubstituted alkyl orcarboxy-substituted or unsubstituted aryl group, R⁶ is a hydroxy group,R⁷ is the following group:

wherein X is a direct single bond or a —O—CH₂— group, m is at least 30mol %, n is at least 20 mol %, the sum of m and n (m+n) is less than orequal to 60 mol %, p is from 2 to 10 mol %, q and r are independentlyfrom 2 to 25 mol %, s is from 1 to 15 mol %, and t is from 15 to 30 mol%.
 11. The element of claim 1 further comprising a colorant dye.
 12. Theelement of claim 1 having a hydrophilic aluminum-containing substrate.13. A method of making a printing plate comprising: A) imagewiseexposing the positive-working imageable element of claim 1 to provideexposed and non-exposed regions, and B) developing the imagewise exposedelement to remove only the exposed regions.
 14. The method of claim 13wherein the imageable element is imaged at a wavelength of from 700 to1200 rim.